S-Nitrosothiols (SNOs) in general - and S-nitrosoglutathione (GSNO) in particular - are stable, potent bronchodilators which also have immune regulatory functions and are present in the normal human airway. Asthmatic bronchospasm is associated with paradoxically low airway SNO levels - and undetectable GSNO levels - despite relatively high concentrations of nitric oxide ( NO) in expired air and upregulation of inducible-nitric oxide synthase. This paradox may be best explained by considering GSNO to be a reservoir of bioactive nitrogen oxides in the airway - as it is in brain and other tissues - the breakdown of which is accelerated in asthma. In this sense, airway SNO catabolism may contribute both to high expired NO concentrations and to bronchospasm in asthmatic patients. This project will test the hypotheses that 1) airway epithelial cells catabolize SNO; 2) the SNO catabolic activity of airway epithelial cells is altered by stimulants relevant to asthma pathophysiology; and 3) airway epithelial cell-mediated SNO catabolism inhibits airway smooth muscle relaxation. A new methodology will be used to study the conversion of SNO to NO in the presence of airway cells. Preliminary data using this system suggest that there are epithelial cell proteins which catalyze GSNO breakdown. These proteins will be characterized with regard to size, sequence, reactant and product stoichiometry and kinetics. Further, the effects of interleukin 4, vasoactive intestinal peptide, dexamethasone, acivicin, aurothioglucose and hemoglobin on epithelial GSNO catabolism and nitrogen oxide transport will be investigated. Finally, the relevance of epithelial GSNO breakdown will be studied in a bioassay of guinea-pig airway smooth muscle relaxation. In summary, this project will test the overall hypothesis that GSNO-mediated relaxation of airway smooth muscle is inhibited in the presence of airway epithelial cells by a regulated protein which catalyzes GSNO catabolism. If this hypothesis is proven, prevention of GSNO catabolism may define new asthma therapies.